The Venom of the Grail War
by Wernher von Braun
Summary: He had sacrificed everything that he had; his identity, his body, and finally his live. All so that he can help Big Boss in granting the Boss' will. But when he was summoned in the Fourth Holy Grail War, he realized something; it was another opportunity to help him.
1. The Legend Return

**The Legend Return**

 **Kotomine Church, Fuyuki City**

As he waits the time to come, Kirei Kotomine once again look at the Command Seals at his hand. He must admit that the fact that he was chosen as one of the Master of the Fourth Holy Grail War kinda surprised him. While he knew about the magecraft, magus, and other things along that line, he never had any connection with them. He then also found out that his father, Risei Kotomine, will be the supervisor of the war, just like in the previous one.

In order to prepare for the war, Kirei learned about magecraft from Tokiomi Tohsaka, who is an old friend of Risei along with the former's father. After receiving an adequate training, Risei and Tokiomi told Kirei the plan that they had made.

Kirei will summon an Assassin-class Servant who is the Hundred-Faced Hassan and Tokiomi will summon an Archer-class Servant who is Gilgamesh. They will sacrificed one of the Hassan and make other Masters think that Assassin is dead. Kirei will then take sanctuary at the church while the remaining Hassans gather information that can be used to defeat other Servants.

At the paper, Kirei knows that the plan is close to perfect and can guarantee easy win. From his experience as an executor however, he knows things can go south and become bad really fast. He can only pray to God that it won't happen and if it does, it won't be too bad.

Anyway, there's perhaps a good thing that can happen by participating in the Holy Grail War. No, it's not the wish-granting device that bears the name of the Cup of Christ. It's something else, or rather someone.

Kiritsugu Emiya.

Kirei once read files about the Masters that will participate in the Holy Grail War. For him, none of them took much of interest. He simply read it so that he has a better chance in case he must fight one of them.

That was until he read the file about Kiritsugu.

When he read about it, Kirei found out that both Kiritsugu and him have one similarity; both of them don't have any goal in life. Everything they did were not to attain one, but to find a goal.

When Kirei found out that Kiritsugu retired from his life as mercenary or freelancer magus, he deduced that it was because Kiritsugu finally found his goal and thus stop looking. Kirei believed that if he talk to the Magus Killer, the result of the conversation can help him in finding the true meaning of his live.

"Kirei, are you ready?"

Kirei turns his head to see that Risei is approaching him. He turns his body to fully faced his father.

"Anytime, father."

"Good. Let us start the summoning ritual then."

* * *

 **Underground**

Inside the room, Kirei stood in front of a summoning circle. The time has come; he's going to summon Assassin and helps Tokiomi in winning the Fourth Holy Grail War.

There's just one problem however; the Holy Grail has been corrupted since the Third Holy Grail War thanks for the Einzbern summoning Angra Mainyu. Due to the corruption, there's a _certain_ thing that has been twisted.

Usually, there are two way to summon a Servant. The first is by using the Master's personality and history. The Grail will then choose the Servant that is the most compatible with the Master. Due to this though, there's a chance of summoning a weal Servant. The second is by using a catalyst which belongs to a Servant when he or she still alive. The problem with using this way is that there's a chance for the Master and Servant aren't a match for each other and can lead to both of them loosing the war.

The way that Kirei used is the second one. This is because he used a catalyst, which is the word "Assassin". That word always refers to someone who killed another person for political reason or payment, which in turn refers to the Hassassin.

That's not what got twisted.

It's the fact that all Servants that had been summoned were heroes from at the least several centuries ago.

With the twist, the Grail doesn't choose one of the Hassan as the Assassin of the Fourth Holy Grail War. It instead choose another heroes to bear the title.

Calling this person a hero however, is quite far fetched.

Another fact is that this person is actually two different people. They just shared the same title during their lives and as such, share each other legends.

The Grail choose one of them. Due to sharing their legend though, there's only little different.

This person is the youngest of all heroic spirits. He's only a year old at the most.

His fame and legend however are not to be underestimated. While normal people might not know much about him, one type of people know, respect, and fear him.

Soldier.

He's the person who's responsible for the spread of Private Forces around the globe. He's also the pioneer of the concept of private military company, soldiers without nation.

He has fought quite a number of supernatural creatures. Some of them were the ghost of the member of an elite team and man who was on fire and driven by nothing but pure hatred.

He's so powerful that everyone believe the only way to have that kind of man is by cloning him.

He's the person who created a nation for soldiers, where they won't be used as tools by country, organization, or government.

He's the Greatest Soldier of the 20th Century and the Man Who Sold the World.

He's also a cardboard box lover, believes in Santa Claus, and quite a foodie.

* * *

Kirei keeps his emotionless face as the smoke from the summoning circle starts to disappear. When all of it finally did, his mind is racing. That's because the man in front of him is definitely _not_ of Middle Eastern descent or dressed in an ancient robes.

The Servant in front of him is a Caucasian male at his late 40's to early 50's. He has a brown hair and full beard at his face which is covered in scars along with blue eye. His other eyes is covered by blindfold that looks like the one usually worn by pirates of the old age. He's wearing a modern combat uniform with urban camouflage. What stand the most are a "horn" at his forehead and his red left arm. The arm seems to be robotic from Kirei's point of view.

Kirei diverts his attention to the man's appearance to the weapons that he carried. His right hand is holding a pistol with extended magazine and suppressor. At his hip is an assault rifle while at his back is a sniper rifle; both of them also have a suppressor attached on their muzzles. At his belt are several types of grenades. There are also some pouches that Kirei believed where the man keeps his ammo.

This man is definitely _not_ Hassan-i-Sabbah.

Before anyone can say anything, the man holsters his gun before giving a salute. He then asks a question with firm and military-like tone.

"Servant Assassin answered to the call of duty. I demand that if you're my Master, identify yourself!"

"Y-Yes, I am your Master." Replied Kirei with a little bit of surprise as he shows his Command Seals.

"Then the contract is complete."

Both Kirei and Assassin look at each other for few moments before Kirei asks something important.

"W-Who are you?" Asked Kirei.

"I am Big Boss."

* * *

 **And the prologue is complete.**

 **As you can see, Venom Snake a.k.a. Big Boss is summoned as Assassin during the Fourth Holy Grail War. Will the change be good or bad? Can the Servants armed with spear and sword face off against Servant armed with modern weaponry?**

 **If you have question or suggestion, feel free to tell me.**

 **Review please.**


	2. Simple Solution

**Simple Solution**

 **Tohsaka Residence**

"Big Boss..." Muttered Risei to himself as he looks at Assassin with both fear and cautious.

When Kirei had reported to him that something...complicated occurred during the summoning, he immediately contacted Tokiomi so that they can see how much this "complication" messed up with their plan. Tokiomi immediately had all of them met in his place with Kirei bringing Assassin with him. Risei was shocked when he saw Assassin thanks to the "horn" at his head. The reason was then replaced when he found out that the man that his son summoned is none other than the Legendary Mercenary.

Said Legend is currently observing all three of them with his one eye while his right hand is right at his holster.

"Assassin, wait outside for a moment. There is much for Risei, Kirei, and I to discuss." Said Tokiomi.

Assassin says nothing in return and doesn't even move an inch. Tokiomit is about to give the same order when Risei raises his hand, stopping Tokiomi.

"Kirei, please order Assassin to wait outside." Said Risei.

"Assassin, wait outside." Said Kirei simply.

While Assassin still say nothing, he goes towards the door and exits the room.

"Well, there goes our plan." Said Tokiomi as he tries to make himself more comfortable.

"Indeed. I would have never imagined that _he_ would be summoned..." Said Risei in return.

"You know about him, father?" Asked Kirei.

"What? You mean you don't..." Realization is given to Risei. "...that's right. You're not the type of people that watched news or listen to the rumors."

Risei takes a deep breath before giving a long explanation.

"Big Boss was a renowned special forces operative and mercenary commander. He also pioneered the concept of private force. Most of Big Boss' fame consists of the creation of his companies – MSF and Diamond Dogs – and his ability to sneak through even a heavily guarded military base without being seen or killing anybody."

Kirei must admit that the last part is very impressive. From how his father spoke about Big Boss, he knows that Assassin was at the very best above average in terms of powers. As such, not killing anybody when infiltrating a heavily guarded military gave him a high risk of being detected. Yet he still did it and succeed.

"As impressive as it is, there's still the fact that Assassin is only one man and as such, prevent us from executing our plan." Said Tokiomi.

"While that's true, this Assassin actually have some advantages." Said Risei.

"Explain."

"Tokiomi, if you're Kirei's enemy and know that he's Assassin's Master, what will be your first thought about the Servant?"

"Remembering the previous wars, I will conclude that...I see."

"There's also the fact that Assassin is using modern weapons, something that most Masters wouldn't have experience with except Emiya. All other Servants would also be from ancient times if everything goes right."

"Which means Assassin would have the advantages of being very unorthodox when fighting from their perspective. Just a question; how pragmatic Big Boss was when he was alive?"

Tokiomi knows that Assassin is a type of Servant that will use even underhanded tactic when fighting. Thus, the more pragmatic the better.

"Kiritsugu Emiya is an angel compared to Big Boss."

Well, that sums it up.

"I see. Since other Masters haven't arrived yet, we better use the time to modify our plan. There will be some changes need to be done thanks to the summoning of another Assassin." Said Tokiomi.

"What should Assassin do in the mean time?" Asked Kirei.

"Hmm... Tell him that he can go around and familiarize himself with the city. But don't attract any unwanted attention."

"Understood."

* * *

 **Few hours later...**

 **Unknown Location**

After familiarizing himself with the city, Assassin decided to goes to an abandoned building. He remembers that, while he never been in Japan before, some of Diamond Dogs' soldiers were. And Fuyuki City was just so happen to be one of few places that Diamond Dogs visited.

Assassin enters the building with a suppressed assault rifle aimed to his front. He scans the inside of the building as he slowly make his way to his destination. So far, he doesn't see anyone enter the building or booby trap.

OK, the booby trap one might be a little paranoid. But after dealing with Cipher, it's a reasonable paranoia.

After exploring the building for few minutes, Assassin finally reach the room he's looking for. He enters it and looks around. He then notices something strange with some part of the wall. He approaches it and then examines it with his right hand. Assassin then punch through the wall with his prosthetic hand. He breaks more of the wall until the hole is big enough for him to pull out a long, wide case. Assassin sets it on the floor before opening it. Inside it is a Killer Bee.

Assassin takes the missile launcher from its container and aims it to somewhere. While this kind of weapon is useless against a being like Servant, the same thing can't be said if Assassin wields it thanks to his skill. He then puts Killer Bee back to its case before exiting the building carrying it.

* * *

 **Few days later...**

 **Fuyuki International Airport**

Assassin is currently at the top of control tower as he waits for the arrival of a pair of Master and Servant. If Kirei – and by extension Risei and Tokiomi – is right, then the Master would be either Kiritsugu Emiya or an Einzbern homunculus.

After waiting for quite a time, an airplane landed on the airport. Assassin takes out his Int-Scope and scans the plane. After a while, people begin to exit the plane. He waits for almost a quarter of hour before a pair of people takes his attention; it's because one of them has crimson eyes and white hair. From the information that he has, almost all Einzbern homunculi share the same appearance.

"So, this is where Kiritsugu was born?" Said the homunculus.

That's it. There's no more doubt that she's an Einzbern homunculus. Assassin diverts his attention to the woman in suit behind the homunculus. On closer look, he can detect that the amount of prana that she has is similar to a Servant.

"Well, Saber. How did you enjoy your journey through the sky?" Ask the homunculus.

" _Saber, huh? Doesn't look so tough. Then again, this same thought got me killed by Solid._ " Thought Assassin.

The rest of the conversation is mundane so Assassin doesn't pay too much attention to it. He keeps his eyes on Saber and the homunculus as they walking through the airport before eventually steps inside a black car. Assassin jumps of the tower and runs to follow the car.

Despite being faster than most if not all types of vehicles thanks for his nature as Servant, Assassin would love to use either D-Horse, D-Walker, or any other vehicles in his disposal. However, all of his vehicles are military type and as such will attract unwanted attention. D-Horse will be too conspicuous in a modern city and D-Walker...he just hope he won't meet any mecha fans.

* * *

 **Few hours later...**

 **Dock**

When he told Kirei that he managed to identify the Einzbern's Servant as Saber, his Master told Assassin to keep an eye on her and try to see if he can get any good clue on her identity. He started to regret following it because everything that happened from the moment they got inside the car to here were all mundane. Not a single clue about Saber's identity, Kiritsugu's location, or anything that can help him winning the war.

Seeing that it's hopeless to get any clue, Assassin puts his Int-Scope back and walks away. After walking for few minutes however, he can feels that another Servant is near and giving an invitation for a duel. Assassin knows that Saber can feel it as well. While Saber and the homunculus walk straight to the location, Assassin takes another route that is longer but provided him a good vantage point. It's also quite covered, decreasing the chances of him being spotted.

When Assassin arrived at the position he wanted, both Saber and the other Servant are had prepared for their duel. Assassin prepares his sniper rifle, M2000-NL, and observes the would-be-battlefield.

The first battle of the Fourth Holy Grail War is about to begin.

* * *

 **And another chapter is done.**

 **Assassin's stats:**

 **Class:** Assassin

 **Alternate Class(es):** Archer, Gunner, Rider, Berserker

 **True Name:**?

 **Alias:** Punished "Venom" Snake; Big Boss; Ahab; V; Big Boss' Phantom

 **Alignment:** Chaotic Neutral

 **Strength:** C+

 **Agility:** D+

 **Endurance:** C+

 **Mana:** E

 **Luck:** C-

 **Class Skills:**

Independent Action: A (It is possible to take action even without a Master. However, to use Noble Phantasms of great magical energy consumption, backup from the Master is necessary.)

Presence Concealment: A+/A++ (It is possible to disappear completely and become almost impossible to be detected. However, efficiency will decrease once preparations to attack are taken. The use of cardboard box increases the concealment stats and giving higher chances of ambushing another Servant.)

Riding: B (Most vehicles can be handled with above average skill. However, cannot ride the likes of Phantasm Races such as Monstrous Beasts.)

 **Personal Skills:**

Battle Continuation: B- (Assassin will do as best as he can to make sure that defeat will not stop him from achieving his goal.)

Bravery: B+ (Only few things can make Assassin stops him by scaring him. One of them is Man on Fire, and for _good reasons._ )

Charisma: B (While never been a king in his life, Assassin once led the infamous Diamond Dogs and Outer Heaven as their leader. As both can be considered a country of soldiers, Assassin's rank is this.)

Disengage: C (Assassin knows when to break away from combat.)

Double Summon: A (Assassin's situation is kind of complicated. In his life, Assassin killed his target with ranged weaponry, making him Archer or Gunner, without anyone knowing it most of the times, making him Assassin, and sometimes approaching or escaping a place using vehicle, horse, or Walker Gear, making him Rider. All of them tend to happen at the same time. When summoned as Assassin, he also possesses class skills of Archer or Gunner and Rider.)

Reflex Mode: C (When spotted, time seems to slow down from Assassin's point of view. This gives him a chance to kill or weaken his opponent for few seconds at the most.)

Marksmanship: A (Assassin is capable of using firearms at their best performances.)

First Aid: B (Assassin is capable of performing first aid on injuries.)

Military Tactics: D (As leader of Diamond Dogs and Outer Heaven, Assassin knows some tactics. However, his the best as solo operator and as such, has a low rank.)

Close Quarter Combat: A+ (Assassin proficiency is in CQC is on the same level as Naked Snake, who himself was trained by the Mother of Special Forces, The Boss.)

Pioneer of the Stars: EX (Assassin pioneered the concept of private forces, modern equivalent of mercenary. Without him, it's not hard to think that mercenary won't be reborn as private forces. This skill actually belongs to Naked Snake, the original Big Boss. Venom Snake possesses this because both Venom and Naked share the legend of Big Boss.)

Body Double: A (Because Venom Snake and Naked Snake share the legend of Big Boss, both of them share the same skills with each other.)

 **Noble Phantasm:**

Arsenal of Diamond Dogs: E-A Rank, Support (Assassin can summon weapons or vehicles that had been used by Diamond Dogs since the time he became its leader. Summoning it however requires mana and the stronger the weapon or vehicle is, the amount of man needed increase. Assassin is also capable of using a real firearms and make it capable of dealing damage to a Servant, provided the type of the weapon once belong to the Diamond Dogs.)

This is Pequod: B Rank, Support (Assassin can summon his trusted pilot, Pequod and his helicopter. Pequod can support Assassin with its heavy armament and can hurt or kill even a Servant, giving it potential to become a nightmare for Servant.)

Buddies: C-A Rank, Support (During his time in Diamond Dogs, Assassin is accompanied by companion called "Buddy". This gives him an ability to summon one of them to his side. His buddies are **D-Horse** , C-Rank mount, **DD,** B-Rank military dog, **D-Walker,** A-Rank Anti-Army Walker Gear, and **Quiet,** A-Rank Anti-Personnel sniper.)

Diamond Dogs: You Are All Diamonds: EX-Rank, Anti-Army (Venom Snake sees Diamond Dogs' members as his family. In return, all of them either share the same view at the best or great respect at the least. This bond gives him ability to summon a Reality Marble which takes a shape of Mother Base at Seychelles Waters. Inside the Reality Marble, Assassin will defeat his opponent with the help of all Diamond Dogs' personnel and buddies, all of them armed with Diamond Dogs' weapons and vehicles. He also has another ability to summon one personnel to real world.) (P.S: Pray to God he doesn't summon _Revolver Ocelot._ )

 **And that is the stats of Assassin. If you feel there's something wrong or need to be added, don't mind to tell me. I am open for suggestion.**

 **If you have question or suggestion, feel free to tell me.**

 **Review please.**


End file.
